1. Field of the Invention
The present invention relates to an engine unit and a motorcycle equipped therewith.
2. Description of the Related Art
Heretofore, a general motorcycle has been known that, due to its limited mounting space, has an engine crankshaft placed in a lateral direction, and has a clutch and a main shaft placed on an axis parallel to the crankshaft. The clutch is connected to one end of the main shaft and transfers power from the crankshaft to the main shaft. Power that is transferred to the main shaft is transferred to a counter shaft (output shaft) that is placed opposite and parallel to the main shaft via a gear mission, and is output to the rear wheel via a drive chain wound around a sprocket attached to one end of the counter shaft. The sprocket is wound by a chain with a gear that rotates the rear wheel and therefore is attached to one end of the counter shaft after an engine unit is mounted on a vehicle with front and rear wheels.
Thus, a sprocket is attached to a counter shaft after an engine unit is mounted on a vehicle, and therefore a clutch that is placed in advance in the engine unit, coaxially with a main shaft placed at a short distance in the front-back direction from the countershaft, is attached to the other end (in the lateral direction) of the end to which the sprocket is attached.
Heretofore, a transmission has been known that is equipped with a plurality of clutches in order to make possible speedy transmission operations of an automobile (see Unexamined Japanese Patent Publication No. SHO58-124851, for example).
Recently, there is a demand for mounting a multi-speed transmission provided with a plurality of clutches and generally mounted on a vehicle, on a motorcycle having limited mounting space. When a multi-speed transmission equipped with a plurality of clutches is mounted on a motorcycle, it is necessary to reduce the size of the transmission itself, and, in addition, due to the structure of the motorcycle on which the transmission is mounted, it is necessary to position the center of gravity approximately centrally in the vehicle width direction together with the mounted engine and create a weight balance that is not biased toward the left or right.
A clutch is a member in the drive transmission system and is comparatively heavy. Consequently, for a multi-speed transmission to be mounted on a conventional motorcycle, there is a demand for positioning a plurality of clutches both to the left and right with respect to a counter shaft and a main shaft that is parallel to the counter shaft, in order to maintain the lateral balance of the transmission itself. That is to say, for a transmission in which a main shaft is placed parallel to a counter shaft at a short distance in the front-back direction, there is a demand for placing one clutch on an extension of one end of a countershaft to which a sprocket is attached.
In other words, there is a demand for an engine unit whereby, even if a clutch and a sprocket that is wound with a drive chain are positioned close on the same side with respect to the center axis of a vehicle on which a transmission is mounted, the sprocket can be attached to a counter shaft after the engine unit is mounted on the vehicle.